1. Field of the Invention
The present invention relates to a stereo endoscope and a stereo endoscope imaging apparatus that enable stereo observation of an object by producing a parallax.
2. Description of the Related Art
Almost all endoscopes visualize an object to be examined, for example, the inside of a body cavity, as a plane without a depth. Conventional endoscopes have difficulties in visualizing the fine irregularities on the surface of an internal wall of a body cavity which are very important diagnostic indices. As a solution of this problem, a stereo endoscope has been proposed. For example, Japanese Patent Laid-Open No. 57-69839 has disclosed a stereo endoscope in which objective lenses are attached to one ends of a pair of image guides, and eyepieces are attached to the other ends thereof. In this stereo endoscope, the two image guides are paired and incorporated in an insertional part of the endoscope. A convergence angle formed by the pair of objective lenses with respect to an observation object point is set to a value that permits stereo visualization. Thus, the inside of a body cavity can be observed three-dimensionally.
The foregoing conventional stereo endoscope is based on a flexible endoscope. In a rigid stereo endoscope, two relay optical systems are arranged in parallel with each other. Optical images provided by the two relay optical systems are picked up using charge coupled devices (CCDs), thus enabling stereo observation.
U.S. Pat. No. 4,924,835 describes a rigid stereo endoscope that includes two photoconductive means and two shutters, wherein two optical images provided by the photoconductive means are intercepted alternately by the shutters in order to enable stereo observation.
The foregoing rigid stereo endoscope includes, as shown in FIG. 1, a pair of optical systems and a pair of imaging devices (CCDs) 71a and 71b. A pair of objective optical systems 72a and 72b facing a region to be observed are incorporated in the distal part of an insertional part of an endoscope 70. The pair of objective optical systems 72a and 72b are spaced to such an extent that a parallax enabling stereo visualization will be created.
Relay optical systems 73a and 73b for transmitting right and left object images are located behind the objective optical systems 72a and 72b. A shielding plate, which is not shown, is placed between the relay optical systems 73a and 73b.
Angling relay optical systems 74a and 74b that transmit the right and left object images while changing the optical paths are located behind the relay optical systems 73a and 73b. Imagery optical systems 75a and 75b for forming the right and left images are located behind the angling relay optical systems 74a and 74b and in front of the CCDs 71a and 71b.
The right and left object images picked up by the CCDs 71a and 71b are converted into electric signals. The electric signals are processed by a signal processing unit 76, and then displayed on a monitor 77.
A procedure of observing a stereo image will be described. That is to say, right and left images are switched at a high speed and displayed on the monitor. An observer wears special glasses, looks at the left image with his/her left eye and the right image with his/her right eye, and thus has a sense of three-dimensionality.
In recent years, another procedure has been proposed: two small image display elements such as liquid crystal displays are employed; a left image is displayed on one of the display elements and a right image is displayed on the other display element; and the right and left images are observed with the right and left eyes respectively. Thus, three-dimensionality is realized.
In either of the above display procedures, for normal three-dimensionality, the endoscope must be focused at a point of the coincident centers of right and left fields of view (intersection between the optical axes of the right and left optical systems ).
In observation using a stereo endoscope, there is a demand for looking at the whole of an object to be observed at a certain distance or observing part thereof in an enlarged scale. To cope with this demand, for example, the conventional endoscope shown in FIG. 1 should be reconstructed in such a manner that zoom optical systems are used as the imagery optical systems 75a and 75b to vary the fields of view.
In the configuration of a conventional stereo endoscope, the right and left optical systems are completely independent of each other. This brings about the following drawbacks:
(1) Minute magnification errors in right and left objective optical systems, relay optical systems, and zoom optical systems are accumulated to appear as a difference in magnification between the right and left optical systems. This becomes outstanding, in particular, when the zoom magnifications are increased.
(2) When the zoom optical systems are used for zooming; that is, when the lenses are moved along the optical axes, movement errors in the right and left zoom optical systems are added to the minute errors described in item (1).
It is hard to bring the errors mentioned in items (1) and (2) under control. As for the zoom optical systems in a conventional stereo endoscope, the right and left zoom optical systems must be interlocked with each other for fear that the magnifications of right and left images may differ from each other. When increased, the magnifications of right and left images differ from each other more critically. In practice, it is almost impossible to control the foregoing errors. A control mechanism would be very complex.
In addition to a zoom-related drawback, there is a problem concerning focusing. The right and left optical systems must be interlocked with each other and focused simultaneously and correctly. This means that a drawback similar to that concerning the zoom optical systems could occur in the conventional stereo endoscope.
In a stereo endoscope, right and left images having a parallax between them are visualized to provide a sense of three-dimensionality. Since the right and left images have a parallax between them, the contours shown in the images are mismatched a bit. However, as long as the displacements of the display positions of right and left images are within an appropriate range, an observer will observe the right and left images as coincident images and have a sense of three-dimensionality, but do not recognize the images as different images. In short, the observer recognizes the right and left images as one stereo image.
However, when the difference in magnification between right and left images exceeds a limit, the sizes of the images differ from each other. The images therefore do not coincide and are seen doubled. At this time, an observer does not recognize the images as a stereo image and feels fatigued very much.
When the inconsistency between the centers of right and left fields of view is too great, the displacements of the display positions thereof increase. The right and left images therefore do not coincide with each other and are seen as different images. When right and left images are out of focus, or for example, when one of the right and left images is in focus but the other one is out of focus (blurred), the aforesaid problems occur.